Please send -log_summary output with performance questions. On Sun, Jul 22, 2012 at 4:01 AM, Bao Kai <paeanball at gmail.com> wrote:
> Hi, Matt, > > I tried ML6.2 with petsc3.3 with default parameters by only specifying > the preconditioner to be PCML. The KSP solver is gmres. > > The convergence rate is much faster, while it still took much longer > time in total. > > For example, for the problem with 500^3 mesh ( 125 million unknowns ) > with 512nodes(4 processors per node) on bluegene/P , it tooks about > ten iterations to get convergent while the total time used is about > 400 seconds. > > 506 the KSP type is gmres > 507 the PC type is ml > 508 KSP rtol = 0.100000000000000008E-04 abstol = > 0.100000000000000001E-49 dtol = 10000.0000000000000 maxit = 10000 > 509 SNES rtol = 0.100000000000000002E-07 abstol = > 0.100000000000000001E-49 stol = 0.100000000000000002E-07 maxit = > 50 maxf= 10000 > 510 0 SNES Function norm 5.859593121800e+02 > 511 0 KSP Residual norm 8.340827070202e+06 > 512 1 KSP Residual norm 7.980806572332e+05 > 513 2 KSP Residual norm 1.870896731234e+05 > 514 3 KSP Residual norm 6.790580947452e+04 > 515 4 KSP Residual norm 2.665552335248e+04 > 516 5 KSP Residual norm 1.130212349885e+04 > 517 6 KSP Residual norm 4.053599972292e+03 > 518 7 KSP Residual norm 1.786770710693e+03 > 519 8 KSP Residual norm 7.313571654931e+02 > 520 9 KSP Residual norm 3.205683714450e+02 > 521 10 KSP Residual norm 1.263243312734e+02 > 522 11 KSP Residual norm 3.945082815178e+01 > 523 1 SNES Function norm 9.378772067642e-02 > 524 0 KSP Residual norm 5.413489711800e+01 > 525 1 KSP Residual norm 1.442598710609e+01 > 526 2 KSP Residual norm 4.073537172140e+00 > 527 3 KSP Residual norm 1.157455598705e+00 > 528 4 KSP Residual norm 3.509855901968e-01 > 529 5 KSP Residual norm 1.160625342728e-01 > 530 6 KSP Residual norm 3.209351890216e-02 > 531 7 KSP Residual norm 7.780869881329e-03 > 532 8 KSP Residual norm 1.820828886636e-03 > 533 9 KSP Residual norm 4.172544590190e-04 > 534 2 SNES Function norm 6.747963806680e-07 > 535 Number of KSP iteration is 9 > 536 SNES solve takes time 406.724867261176314 > > But with bcgs and bjacobi, it tooks about 550 KSP iterations ( 2 snes > iterations ) and 69 seconds to get the result. > > For much smaller problems, benefiting from the fast convergence, it > did takes less time to get the result. It seems that the ml can not be > scaled, or I used it in a wrong way. > > Best Regards, > Kai > > > > Message: 2 > > Date: Sat, 21 Jul 2012 08:47:10 -0500 > > From: Matthew Knepley <knepley at gmail.com> > > To: PETSc users list <petsc-users at mcs.anl.gov> > > Subject: Re: [petsc-users] How to investigate the reason for slow > > convergence rate? > > Message-ID: > > < > CAMYG4GkfV6kmTFEKXUadOv+2CrKHk9hRY7UR-cFWf+vcRxCv5g at mail.gmail.com> > > Content-Type: text/plain; charset="iso-8859-1" > > > > On Sat, Jul 21, 2012 at 4:30 AM, Bao Kai <paeanball at gmail.com> wrote: > > > >> > >>> HI, all, > >> > >> I am still suffering from the slow convergence rate of the KSP solution. > >> > >> I changed the code to use Petsc3.3 and then try the gamg precoditioner, > >> the convergence rate is better, while it took more total time because it > >> took much more time for each iteration and some extra time for > >> pre-processing. > >> > > > > Try ML to see if it has better defaults for your problem. If not, you > will > > have to start experimenting with the solver > > parameters. > > > > > >> I am wondering if there are some ways that can help me to investigate > the > >> slow convergence rate for KSP solution so that I can do some > improvement. > >> Is DMMG will be a good solution? > >> > > > > No. > > > > Matt > > > > > >> Thank you very much. > >> > >> Best Regards, > >> Kai > >> > >>> > >>> Message: 2 > >>> Date: Wed, 11 Jul 2012 15:17:15 -0500 > >>> From: Matthew Knepley <knepley at gmail.com> > >>> To: PETSc users list <petsc-users at mcs.anl.gov> > >>> Subject: Re: [petsc-users] Does this mean the matrix is > >>> ill-conditioned? > >>> Message-ID: > >>> <CAMYG4Gk7T= > >>> q+w1PKO7G_TW07iDzux90Sncbv9K7d0FD-MDrLRg at mail.gmail.com> > >>> Content-Type: text/plain; charset="iso-8859-1" > >>> > >>> On Wed, Jul 11, 2012 at 12:40 PM, Bao Kai <paeanball at gmail.com> wrote: > >>> > >>> > Hi, all, > >>> > > >>> > The following is the output from the solution of a Poisson equation > >>> > from Darcy's law. > >>> > > >>> > To compute the condition number of matrix, I did not use PC and use > >>> > GMRES KSP to do the test. > >>> > > >>> > It seems like that the condition number keep increasing during the > >>> > iterative solution. Does this mean the matrix is ill-conditioned? > >>> > > >>> > >>> Generally yes. Krylov methods take a long time to resolve the smallest > >>> eigenvalues, so this approximation is not great. > >>> > >>> > >>> > For this test, it did not achieve convergence with 10000 iterations. > >>> > > >>> > When I use BJOCABI PC and BICGSTAB KSP, it generally takes about 600 > >>> > times iteration to get the iteration convergent. > >>> > > >>> > Any suggestion for improving the convergence rate will be much > >>> > appreciated. The solution of this equation has been the bottleneck > of > >>> > my code, it takes more than 90% of the total time. > >>> > > >>> > >>> Try ML or GAMG. > >>> > >>> Matt > >>> > >>> > >>> > Thank you very much. > >>> > > >>> > Best Regards, > >>> > Kai > >>> > > >>> > >>> > >>> > > > > > > -- > > What most experimenters take for granted before they begin their > > experiments is infinitely more interesting than any results to which > their > > experiments lead. > > -- Norbert Wiener > > -------------- next part -------------- > > An HTML attachment was scrubbed... > > URL: > > < > http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120721/eaf7b2ee/attachment-0001.html > > > > > > ------------------------------ > > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120722/7f782dd6/attachment-0001.html>
